1. Field of the Invention
The present invention relates to a compact illumination system utilizing a light source such as an array of light emitting diodes (LEDs) or laser diodes (LDs) consisting of longer life span in the case of a projection display device employing the illumination system.
2. Description of the Related Art
Referring to FIG. 1, a conventional projection display device includes a light source 100; a collimating lens 110 which makes a light beam emitted from the light source 100 parallel; light split units which split a white light beam from the collimating lens 110 into red (R), green (G), and blue (B) light beams, respectively; first through third liquid crystal display (LCD) panels 180, 181, and 182 which perform an on/off process on the R, G, and B light beams, respectively, forwarded from the light split units to form color images; a dichroic prism 190 which combines the R, G, and B light beams respectively transmitted through the first, second, and third LCD panels 180, 181, and 182; and a projection lens system 200 which magnifies and projects the image formed by the R, G, and B light beams on a screen (not shown).
The light split units include a first dichroic mirror 120, which transmits the R light beam in the white light beam emitted from the light source 100 and reflects the remaining G and B light beams, and a second dichroic mirror 140, which transmits the B light beam reflected from the first dichroic mirror 120 and reflects the G light beam reflected from the first dichroic mirror 120. In addition, the light split unit also includes a first mirror 130 which reflects the R light beam transmitted through the first dichroic mirror 120 on the first LCD panel 180, a second mirror 150 which reflects the B light beam transmitted through the second dichroic mirror 140, and a third mirror 160 which reflects the B light beam reflected from the second mirror 150 on the third LCD panel 182. Meanwhile, first, second and third focusing lenses 170, 171, and 172 are respectively disposed between the first through third mirrors 130, 140, and 160 and the respective first through third LCD panels 180, 181, and 182.
In a projection display device having the above-described structure, a white light beam emitted from the light source 100 is split into R, G, and B light beams, the R, G, and B light beams are processed by the respective first through third LCD panels 180, 181, and 182 according to previously input image signals to form different color images. The R, G, and B color images are combined into a single image through the dichroic prism 190, and the combined image is formed on the projection lens system 200 and magnified and projection on a screen.
The conventional projection display device utilizes, for example, a xenon lamp, a metal-halide lamp, or a UHP lamp as the light source 100. Such lamps generates heat of a high temperature of about 500° C. Thus, a separate cooling fan is used in order to cool the heat. However, this cooling fan is the principle cause of noise and disturbs users when the they are exposed to the hot air discharged from the cooling fan. Moreover, the lamps emits a large amount of ultraviolet rays and infrared rays which are harmful to the users. Thus, an optical filter for infrared rays and an optical filter for ultraviolet rays are required to prevent them from being emitted. Accordingly, the entire volume of the display device increases while the manufacturing cost also increases.
In addition, the lamps have a spectrum in which all wavelengths widely spread to thus have a narrow color gamut, thereby limiting color selection and degrading color purity. Moreover, the average life span of the lamps is short, which affects the stable use of the lamps.